The present invention relates generally to machining, and, more specifically, to electrical erosion machining.
Gas turbine engines include various rotor blades and stator vanes having specifically configured three-dimensional (3D) airfoils for compressing air and extracting energy from hot combustion gases. Each airfoil has a generally concave pressure side and an opposite generally convex suction side extending axially between leading and trailing edges from root to tip of the airfoil along its radial span.
Each airfoil has axial curvature represented by its camber line, and may twist from root to tip as required for maximizing aerodynamic performance. Fan blades are relatively large and typically have the greatest amount of twist from root to tip in the gas turbine engine.
Each airfoil stage in a gas turbine engine includes a multitude of airfoils extending radially outwardly from a supporting rotor disk. Each airfoil may be individually manufactured and includes a dovetail at its root end sized to engage a complementary dovetail slot formed in the perimeter of the rotor disk. In another configuration, the airfoils are directly formed integrally with the rotor disk in a one-piece or unitary assembly commonly referred to as a blisk.
The rotor blisks have various advantages but require special manufacturing thereof. A solid workpiece disk blank is initially machined to form a row of rough airfoils, which are then finally machined to the precise final dimensions required for intended performance.
Since the complete row of blisk airfoils is made from an initially solid workpiece blank, a substantial amount of material removal is required to achieve the desired final-dimension airfoils thereon. Accordingly, rough and finish machine equipment are required for manufacturing blisks, with attendant overhead and manufacturing costs associated therewith. And, the substantial amount of material removal from the disk blank requires a corresponding amount of machining time and subjects the machining equipment to corresponding wear.
Airfoil blisks are typically manufactured using conventional multiaxis numerically controlled milling machines or electrochemical machines. In a milling machine, a rotating cutter is used for cutting away metal in stages to first roughly form the individual airfoils followed in turn by finish machining thereof. Typically, finish smoothing of the airfoil surfaces by hand grinding or smoothing processes is also required.
In electrochemical machining, a pair of cathode electrodes having the desired final surface shape of the two sides of the individual airfoils are used to electrochemically erode metal from the airfoil blanks which are powered as anodes, with a suitable electrolyte being channeled therebetween for effecting electrochemical erosion. The advantage of electrochemical machining is the ability to form the final airfoil surface finish with little, if any, post-processing thereof.
However, both milling and electrochemical machining require varying amounts of time to complete an individual blisk with its full complement of individual, 3D airfoils thereon.
Accordingly, it is desired to provide a new method and apparatus for machining a complex workpiece, such as a blisk, with a greater rate of material removal therefrom.
An electromachining apparatus includes a mandrel for supporting a workpiece next to a cutter mounted on an arbor. The workpiece is powered as an anode and the cutter is powered as a cathode, and a coolant is circulated therebetween. The cutter is rotated and plunge twisted into the workpiece to form a twisted slot therein, with adjacent ones of such slots forming twisted blanks therebetween. The individual blanks may then be subsequently machined to final shape such as an airfoil configuration.